The overall objective of this project is to understand the mechanism by which the head of bacteriophage T4 is assembled and filled with DNA. We will concentrate on the mechanism of proteolytic cleavage of the phage capsid and core components which occurs during the assembly process. Assembly-associated proteolytic cleavage is of general interest because it occurs for a variety of phage and animal viruses. Recent studies from this laboratory have revealed two previously undetected processed phage proteins designated pip and pZ. The pip protein has been identified as the precursor of internal peptide II found in mature phage particles. The pip protein is distinct from other known components of the assembly core (the three internal proteins and the gene 22 protein) and distinct from the gene 21 protein, a processed form of which functions as the protease in the cleavage of all known processed proteins of T4. These studies will be continued with the following specific aims: (1) To investigate the possibility, suggested by indirect evidence, that other proteases, either phage or host controlled, play a role in the cleavage of T4 proteins; (2) To determine whether the pip protein and pZ (or its processed form pZ*) are components of the phage capsid or of the assembly core; (3) To identify the phage genes which code for pip and pZ and determine whether these proteins serve essential or non-essential functions; and (4) Continue collaborative sequence studies on species variants of the internal peptides and their precursors. BIBLIOGRAPHIC REFERENCES: Identification of gene products required for in vitro formation of the internal peptides of phage T4. Goldstein, J.G., McCullough, J.E., and Champe, S.P. 1976. J. Virology 18:894-903. Role and location of "Protease I" from Escherichia coli. Kowit, J.D., Choy, W.N., Champe, S.P. and Goldberg, A.L. 1976. J. Bact. 128:776-784.